non-metal n.

a prefix used freely in English and meaning "not, lack of," or "sham," giving a negative sense to any word, 14c., from Anglo-French noun-, from Old French non-, from Latin non "not, by no means, not at all, not a," from Old Latin noenum "not one" (*ne oinom, from PIE root *ne- "not" + PIE root *oi-no- "one, unique"). In some cases perhaps from Middle English non "not" (adj.), from Old English nan (see not). "It differs from un- in that it denotes mere negation or absence of the thing or quality, while un- often denotes the opposite of the thing or quality" [Century Dictionary].

an undecomposable elementary substance having certain recognizable qualities (opacity, conductivity, plasticity, high specific gravity, etc.), mid-13c., from Old French metal "metal; material, substance, stuff" (12c.), from Latin metallum "metal, mineral; mine, quarry," from Greek metallon "metal, ore" (senses found only in post-classical texts, via the notion of "what is got by mining"); originally "mine, quarry-pit," probably a back-formation from metalleuein "to mine, to quarry," a word of unknown origin. Perhaps related somehow to metallan "to seek after," but Beekes finds this "hardly convincing."

The concept was based on the metals known from antiquity: gold, silver, copper, iron, lead, and tin. As an adjective, "of or covered with metal," from late 14c. As short for heavy metal (rock music) by 1980. Metal-work "work, especially artistic work, in metal" is by 1724.